Grid controlled polyphase rectifier



June 14, 1949.

F. OBLOY GRID CONTROLLED POLYPHASE RECTIFIER Filed July 24, 1947 IN V ENTOR.

4 9 BY e414 l I J g Patented June 14, 1949 STATES: PATENT OFF I CE GRIDCONTROLLED POLYPHASERECTIFIER Felix A; obloy Garfield Heights, OhioApplicationJuly 24-, 1947, Serial No. 763,218

Claims. 1.

This invention. relates topolyphase alternating current rectifiersandhasfor a primaryobject to provide a rectifier. withcircuits thatvwill provide a'selfw regulated constantdirect current output under.changing-load conditions.

A. more particular object. of the invention. is to provide a polyphaseA: C. rectifier. with a-polyphase-shift. grid control. circuittforobtainingv a selfregulatedeonstant voltage. D, C. output under changinglo ad conditions.

Another object-of the invention isto provide a polyphase A. G.rectifierin which-.theself regulated output D. C.-voltage isnot-afiected by line voltage fluctuations A. further object-of theinventionis to provide a polyphaseA. C.: rectifier. with time delay.circuits to insure maximum tube life andefiiciency.

Another object'ofthe. invention is to provide a polyphase A. C.rectifier with a polyphaseshift grid control circuit in which the gridcontrolst-abilityis unaffected by changing load conditions.

A more specific object 'of the invention is to provide a=-polyphase A.C. rectifier incorporating auxiliary timedelay: circuits to-permit thevarious tubecathodes to be heated sufficiently before the rectifierwill-deliver current to. a load.

This rectifier-has'been particularly useful in connection with Drcimotors driving heavy machine tools. Itwill promote and give a lineartorque curve performance evenunder constantly changing loadconditions-on such machines. As a. result a smoother finish isobtainedonthe work piecesby the machine tool and-.inmany instances thefinish is fine enough to preclude additional surface-finishingoperations.-

With theaforementionedand other. objects in view the invention-residesin the combination of parts and details-of constructionset .forthin thefollowing specification andappencled claims, certain embodiments thereofbeing. schematically shown in. the. accompanyingv drawing. which is. aschematic circuit layout..of oneformotthe invention.

Athree phase. power system I isshown leading into a mainswitch 2..Suitable fuses-3f are provided intheswitch. Connectedtoone phase of thepower. supply I throughswitch 2" by means of lines 4 and 5' is a timeclock 6. Upon manual closing of switch Ttime'clock Gi's energized with astepped. downvoltage by means of a voltage divider .1. When. the 5Onsetting, of the time clockis reached, relay 8' is energized sufiicientlyto close contacts 9 and) which in turn energizes relay I I through linel2 When relay H is. energizedswitchli 3' is closed and A. C. current isthen available tosupply the rectifier. Series-parallel connected'to'terminals 1'4 and [5" by lines I6. and IT respectively .arethe primarycoils 18,? I9, 20.. and 2110f. a transformer 22. Secondary coils 23;.24,25 and"26 furnish a cathode heater supply source. Directly connecteda-cross primary coil 2 I by lines 2-1 and 28 is a cooling fan 29; Lines21 and 28 also feed a second time clock 30'.

' Connected by lines 31, 32' and 33 to terminals 14,15 and 3.4.ofswitchl3 are the primary'coil's 35;. 36' and 3'! of 3 single phasetransformers-38 deltaconnected'. The se'condaries39, 40 and 4| areconnected to maximum power taps 42, 43 and 44.. These. taps areconnected by lines 45, 463 and 4''! to terminals'4'8, 49 and.'50"onterminal block 5|. Also provided on block 5| are terminals 52,v 53 and54" which. are connected by lines 55, 56 and 5T'respectively to' taps58;59' and '60. which in turn are positioned equally 'at'less than the fullpower settingion each secondary 39', 4'0" and 4f. Terminals; 48,49 and50' are; further connected. by lines 6 l, 62' and" 63 to' terminals -64,'65 and fifilrespectively, by a. switch .block: 61.

When time clock. 3llreaches" its On? setting, coil 68' is energizedand'closes a pivoted contact B-Q-Jagainst fixed contact". 10. Currentthen flows from. line 32 through aline TI to a relay coil 12'. The otherside of the. coil. is connected to line 33. Connected across .lines3'3and H by linesl3 and T4 is a panelfllight 15. When relay coil .12 isenergized a switch. 16 is'closed against terminals 64,65 and 66... Thisclosing. permits current from lines 6|, 62' and 63 to flow pasttheswitch block 61 to lines T1,.181and19which are jointed to the plates.80",'. 8| and 820i rectifier tubes 83', 84 and 85,. respectively.

Each tube. contains, a screen grid element 86 and a cathode 81' the twobeingconnected by a line 88. Each tube also contains a'heaterelement 89connected as indicated by letters X1,'.X2, to the secondaries 23124; 25;26' of transformer 2'2. Between the screen grid element andthe cathodein eachtube are control grid elements 90', 9| and'92". Micacondensers93; 94 and- 95 connected as shown between the control grids and cathodesin each tube stabilize the control grids and maintain them at a negativepotential. A line 96. is. connected from control grid 90' of tube83 toplate line 11' andiincl'udes a condenser 91', a potentiometer. 98,. afixedlresistor 99, and a seco'nd'condenser i002 A line Hill is connectedbetween control. grid. 9| of tube '84 to plate line 19" and includes apotentiometer. 102; a fixedresistor I03i'anda condenser i04",.ailofwhich are 3 identical in rating with the similarly placed units in theline 95 of control grid 90. Line I! is coupled to line 96 by a condenserI05.

A line I06 is connected from the control grid 92 in tube to its plateline I9 and includes a condenser I01, a potentiometer I08, a fixedresistor I09 and a second condenser H0, all of which are identical inrating with the similarly placed units in grid control circuits of theother two tubes.

The cathodes 80 of the tubes 83, 34 and 05 are connected by lines III toa common line H2. Inserted in line H2 which leads to positive load.terminal H3 are an ammeter II4, a choke coil H5, and a fuse H6. Thenegative load terminal i I1 is connected by line II8 to the secondariesof transformer 38. Interposed in line H8 is a protective fuse II9. Avoltmeter I and two parallel connected lamps I2I are connected acrosslines H2 and H8.

The combinations of condenser I00 and resistor Gil, condenser I04 andresistor I 03, and condenser I I9 and resistor I09, act as ionic shockabsorbers in the commutation cushion circuit formed by the control gridand plate of each tube by lines 96, MI and I06. As previously mentionedthe condensers 93, 94 and 95 maintain a negative potential on each grid.The A. C. grid voltage for phase-shift displacement is evident betweentubes 83 and 05. The plate current from plate 80 flows through ionicshock absorber combination condenser I00 and resistor 99 throughpotentiometer 538 and condenser II to control grid 90. Since tube 83 iscoupled to the control grid 9| of tube 8 by the condenser I 05 in orderto maintain the phase shift voltage relationship between individualanode control potentiometers I02 and 98, the output voltage is adjustedwhile potentiometer I08 is set at its maximum voltage position for thetube 85 grid current of ionization.

Since the grid circuit of all three control grids is series closed ordelta type interlocked with the ionic shock absorbers, grid currents ofionization on all control grids are proportional in respect to loadrequirements. Load surges on anodes 80, 8| and 82 lower the I R dropsand potential conditions on potentiometers I02 and 08. The instantaneousvoltage rise characteristic is applied on control grids 90, 9| and 92,and the effective grid current of ionization efiects an instantaneouscommutation. Consequently a constant voltage output with instantaneousvoltage regulation is obtained by the rectifier.

Any receding current requirements will not affect output voltage becauseof the phase-shift retardation on potentiometers I02 and 98. P0-tentiometer I08 is a Vernier voltage adjustment and is always set to itsmaximum voltage position with regard to tube 85.

The lamps I2I are used as a minimum linear resistive load to permit useof the rectifier where load conditions may be only in the order of a fewmilliamperes. Under such an extremely low load requirement voltageranges and controls operate with a slight loss of voltage range.

The feature of the rectifier regarding long tube life and efliciency isobtained by an inverse peak voltage minimizing effect of the ionic shockabsorbers previously described. Peak inverse voltage conditions lead thenormal sized positively charged ions to be attracted to the anodes inthe conventional manner but the larger sized positively charged ions,when they go through this extreme potential drop, accelerate themselvesgreatly and impinge upon the plates of the vari- '4 ous tubes withdamaging effect. Also the disturbances thus caused lead todisintegration of the cathodes of the tubes with a consequent loweringof effective emission tending to approach total tube failure.

To overcome such detrimental effects to the tubes in this rectifier therelated voltage on grid phase shift retardation is constantly triggeredby a series connected ionic shock absorber which limits or dampens thespeed of the large size positively charged ions to a low rate ofionization or bombardment. Also, secondary ionic emissions are held at alow level through the blocking action of the screen grids 86. Thiscushioning or dampening effect promotes ionic control and stabilityeliminating the possibility of any damage to the plates anddisintegration of the cathode surface which normally results from sharpfluctuations in load requirements.

The system as shown is connected to a three phase, 220 volt 60 cyclesource I. The lines SI, 62 and 63 as shown connected to terminals 48, t9and 56 on block 5| make possible a regulated D. C. output voltage over arange of 180 to 250 volts. If the lines 6|, 62 and 63 are connected toterminals 52, 53 and 54 the D. C. voltage is changed to a range of tovolts. This change in range is effected by the changeover from maximumto partial tap positions on the secondaries 39, 40 and 4| of transformer38.

A polyphase rectifier is thus provided which insures long tube life, hasno phase-back or arcback deficiencies, gives no change in voltage outputdue to line voltage fluctuations, maintains a constant torque curvelinearity in response to continuously varying D. C. load conditions, hastwo voltage ranges and has reliable and trouble free grid controlstability, unaffected by any type of load application.

I claim:

1. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage, comprising time delay means for controlling theflow of current through said rectifier, rectifying tubes each includinga control grid for changing an A. C. input to a D. C. output, meansassociated with said time delay means to prevent current flow from thetubes until said tubes have been predeterminedly heated, and means forin stantaneously varying the effective grid current of ionization ineach tube through its control grid in response to varying loadconditions to obtain a D. C. output voltage at a preadjusted constantlevel.

2. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising a plurality of rectifying tubes eachincluding a control grid for changin an A. C. input to a D. C. outputand control means for instantaneously varying the effective grid currentof ionization of each tube through its control grid for obtaining a D.C. output voltage at a preadjusted constant level.

3. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output. voltage comprising a plurality of rectifying tubes, eachhaving a cathode and a plate, a control grid for each of said tubes andionic shock absorber means interconnected between the control grid andplate of each tube for preventing detrimental ionization conditions inthe tube due to varying load conditions.

4. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising a plurality of rectifying tubes eachhavamazes:

ing a cathode..andii'alplataiaicontrol grid for eachof said tubes,voltage adjusting means. in series with each of said control: grids'andan ionic shock absorber means interconnected between the plate andcontrol. gridlof each' tube and including said voltage adjusting meansin series therewith for preventing detrimental effects to the plate, andcathode infthe. tubes due toheavy positive ionbombardment under varyingload conditions.

5. A polyphase grid controlled rectifier for supplying: a'self-regulatedD. C. output voltage comprising. va plurality of rectifyingtubes eachhaving a plate and a cathode, a control grid for each of said tubes, anegative bias means connected between the control grid and the cathodein each tube, voltage adjusting means connected to each of said controlgrids and an ionic shock absorber means interconnected between the plateand control grid of each tube including said voltage adjusting means inseries therewith for preventing detrimental ionization conditions in thetubes due to varying load conditions.

6. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising a plurality of rectifying tubes eachhaving a plate and a cathode, a control grid for each of said tubes, anegative bias means connected between the control grid and the cathodein each tube, voltage adjusting means in series with each of saidcontrol grids and an ionic shock absorber means associated with thecontrol grid and the plate of each tube and in series with said voltageadjusting means for preventing detrimental ionization conditions in thetubes due to varying load conditions and time delay means associatedwith said rectifying tubes for preventing tube operation before thecathodes of said tubes are sufficiently heated.

'7. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising three rectifier tubes each having aplate, a cathode, a screen grid, a control grid and a heater,transformer means for supplying current to the heater of each tube, asecond transformer means for supplying A. C. power to said tubes, timedelay means to prevent A. C. power supply to the tubes until said tubesare sufliciently heated, a pair of output terminals for load connectingpurposes, means connectin one of said terminals with the cathodes of thetubes and the other terminal with said transformer means, a condenserconnected between the control grid and cathode of each tube to maintaina negative potential on the control grid, an ionic shock absorber inseries with a line from the control grid to the plate of each tube, apotentiometer to adjust the voltage across each tube, one of saidpotentiometers being set at its maximum voltage setting while the othertwo potentiometers are adjusted to get a phase-back voltage relationshipacross the other two tubes, and means to interconnect the three controlgrids in a series closed or delta relationship interlocked with saidionic shock absorbers so that the grid current of ionization on allcontrol grids is proportional to the varying requirements of outputcurrent at the load terminals.

8. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising three rectifier tubes each having aplate, a cathode, a screen grid, a control grid, and a heater, means tosupply current to said heaters, means to supply A. C. power to saidtubes after a time delay while said heaters are warming up 6. saidtubes, a condenser connected-betweem the' control grid and cathode ofeach tube. tomain taina negative potential on the control grid, a lineconnecting each control grid with the plate of-its tube, a condenser anda resistor connected in series in said line for acting jointly as ionic:shock absorbers, a potentiometer and a second" condenser in series insaid lines to said control. grids ofthe first and third tubes, apotentiometer in series in said line connected to the c'ontrok grid ofthe second tube, a condenser coupling the gridconnected lines of thefirst and second tubes and means to maintain a phase shift'voltagerelationshipbetween the anode control potenztiometers of the first andsecond tubes which comprises adjusting the output voltage by means ofthe first and second tube potentiometers while maintaining thepotentiometer of the third tube at its maximum voltage setting.

9. A polyphase grid controlled rectifier for supplying self regulated D.C. output voltage comprising a plurality of rectifier tubes, means tosupply an A. C. input voltage to said tubes, means to delay conductionby said tubes until they are sufllciently heated, means associated withsaid tubes to maintain a phase shift voltage relationship between onetube and the other tubes and means associated with each tube to controlthe ionization rate in each tube in response to varying load conditionsto prevent detrimental effects to the tubes.

10. A polyphase grid controlled rectifier for supplying a self regulatedD. C. output voltage comprising three rectifying tubes each having aplate, a cathode, and a heater, a control grid in each of said tubes, aline connecting each control grid with the plate in each tube, acondenser and a fixed resistor in series in each of said lines to act asan ionic shock absorber for their respective tubes, a second condenserand a potentiometer connected in series in the lines of two of saidtubes, a potentiometer in series in the line of the third tube forregulating the output voltage setting of the tubes, a condenser forcoupling the third tube line to the line of one of the other two tubes,a condenser connected from the control grid to the cathode of each tubefor maintaining a negative potential on said control grid, a manualswitch for connecting the rectifier to a three phase A. C. power source,a time delay clock being energized by the closing of said switch, asecond switch being subsequently closed by energy controlled by saidtime clock, a transformer having primary coils and secondary coils,means connecting said secondaries with the heaters of the tubes, asecond time delay clock, a cooling fan, means connected across one ofthe primary coils of the transformer for energizing said fan and saidsecond clock, a second transformer having primary coils and secondarycoils, means to connect said primary coils to the time clock controlledsecond switch, maximum and intermediate taps for providing maximum andreduced supply voltage connected to each of the secondaries of saidsecond transformer, a terminal block, two sets of terminals in saidblock, means for connecting one set of terminals with the maximum tapsand the other set of terminals with the intermediate taps, a switchblock, means to connect said switch block with either set of terminalson the terminal block, a switch on said switch block, means responsiveto the time setting of said second time clock for energizing said lastnamed switch and closing same thereby, means connecting said last named7 t switch for delivering current to the plates of each tube upon theclosing of said switch, a positive output terminal, a negative outputterminal, means connecting the positive terminal to the cathodes of eachtube, a choke coil and an ammeter in series with said last namedconnecting means, means connecting the negative output terminal with thesecondaries of the second transformer, a voltmeter connected across saidoutput terminals, a linear resistance connected across said outputterminals, protective fuses in each connecting means to said outputterminals and protective fuses connected between the manual switch andthe first time delay clock.

FELIX A. OBLOY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,893,784 Prince Jan. 10, 19332,186,815 Alexanderson Jan. 9, 1940 10 2,095,047 Winograd Oct. 5, 1947FOREIGN PATENTS Number Country Date 782,352 France Mar. 18, 1935

